A.P.
Yes, this is a big deal. She is reacting to feelings of no control - to frustration - to anger. She needs to learn proper ways to react to these feelings as they are a part of life. She needs to learn new behaviors to replace these with. She is so overwhelmed by these feelings that holding them in is not an option. She needs to release them - she just doesn't do it in a safe way. I'd speak to my pedi and get a referral to a counselor or therapist who is much more knowledgeable about this than I am. In the meantime, I'd work with my daughter and explain that it's okay to get angry. Everyone gets angry. It is NOT okay to hurt yourself, others, or property. Perhaps you can give her the strategy of blowing air out of her mouth as hard as she can when she gets mad, instead of hurting herself. Maybe teach her to count to 10. Maybe you can designate a space in your house where she can go when she's mad to "Cool Down" - a safe place. Let her yell into a pillow, hit a pillow? I'm not sure, but something where she can let it out but not hurt anyone or anything (including herself).
Best of luck to you! Let us know how it goes...